Untitled dates from a crucial moment in Robert Irwin’s career when his perception of art, and of perception itself, were being reshaped. His concerns led him in 1966 to the convex disc format, which resulted in the body of work that gained him an international reputation. Irwin has explained that he adopted the circular shape because the traditionally rectilinear format of painting no longer made sense to him.

Formed of acrylic resin, Untitled is a convex disc that projects, by means of a clear plastic tube, twenty-four inches from the wall. Multiple coats of a...